This invention relates to a control signalling arrangement for a digital transmission system and more particularly to a control signalling arrangement that transmits by way of a command channel superimposed on a system parity channel.
Line monitoring and fault locating functions are used in the prior art to maintain a digital transmission system. One method used for line monitoring is to determine a bit error rate by inserting at the transmitting terminal a block parity bit in a predetermined position in the data stream after each block of data. Each block of data and its block parity bit are analyzed for block parity violations at the receiving terminal or at an intermediate point along the line. Any block parity violations are countered over a period of time and are computed into a bit error rate. One arrangement for line monitoring in accordance with the foregoing description has been disclosed in U.S. Pat. No. 4,121,195.
Fault locating is a procedure used for determining which repeater section of the line is the source of a trouble condition when the line monitoring arrangement indicates there is an inordinately high bit error rate.
A problem with the prior art line monitoring and fault locating systems is that they are separate from the main transmission system and add significant expense to the construction and operation of the system.